Identification, characterisation and analysis of the Oltrepo Pavese calanchi in the Northern Apennines (Italy)

Badlands are characteristic erosional forms distributed along the entire Apennines. In the Italian context badland areas are called “calanchi”, the plural of the word “calanco”. In this paper we present the first calanchi inventory map of the Oltrepo Pavese area, Northern Apennines (Italy). In total 263 calanchi were mapped using remote sensing techniques like Orthophotos, Google Earth images, as well as field recognition. Moreover, calanchi were characterised from a geomorphologic, geologic and a morphometric point of view. The calanchi of the Oltrepo Pavese have been categorised in two geomorphological classes based on process related morphologies. In the study area calanchi mainly occur in soft sedimentary bedrock materials such as melanges, marls, claystones, and interstratified rocks. The results show that calanchi formations are often related to faults and tectonic lineaments present in the study area. Moreover, we analyse a 5 m cell size Digital Terrain Model to detect correlations between calanchi and morphometric indices. The calanchi, defined and categorised for the first time in the study area, show typical morphometric characteristics of Apennine calanchi forms and features. In particular, they occur on concave south-facing slopes on soft bedrock formations. Finally, a multitemporal air photo interpretation over a 40 years period indicated a general decrease in calanchi areas. The area reduction is mainly correlated to intensive land use changes combined with variations of precipitation pattern. The revegetation trend was also confirmed by NDVI analysis based on Landsat satellites images. The calanchi were digitized and stored in a GIS database providing the information for future quantitative modelling assessments.